Thermostatic switch



May 20, 1958 R. D. GRAF ET AL 2,835,767

THERMOSTATIC SWITCH Filed May 16, 1957 2 Sheets-Sheet 1 Z 7 B/ME TA L 38 (INSULATION 1a 2/ 26 20 43 /0 4NSULAT/ON 5 I .L E; E

//v VEN TOR 5 ROBERT D. GRAF LEO L. WEBER AGENT May 20, 1958 D GRAF ETAL 2,835,767

THERMOSTATIC SWITCH Filed May 16, 1957 27 24 (BIMETAL 2 Sheets-Sheet 2 //\/\-/EN7'O/?S ROBERT D. GRAF LEO LfiWEBER AGENT nited THERMOSTATIC SWITCH Robert D. Graf, Flora, and Leo L. Weber, Logansport, Ind, assignors to Essex Wire Corporation This invention relates to thermostatic switches and more particularly to bimetallic snap-acting thermostatic switches.

An object of the present invention is the'provision of a thermostatic switch which is particularly adapted for use with electrically heated blankets.

Another object of the invention is to provide an improved thermostatic switch of the snap-acting type which may be inexpensively and accurately calibrated.

An additional object of the present invention is to provide a thermostatic switch employing a simple bimetal member having a fiat shape which may be simply deformed after assembly in the switch to have a snapacting movement upon both break and make of the switch contacts.

A further object of the invention is to provide a thermostatic switch having manual control means for readily adjusting and varying the temperature at which the switch operates to control an electrically heated object.

Other objects and features of the inevention will be apparent from the following detailed description with reference to the accompanying drawings wherein:

Figure l is a top plan view of a thermostatic switch embodying the invention.

Figure 2 is a side elevational View of the switch shown in Figure 1.

Figure 3 is a perspective view of the major portions of the switching mechanism of the switch shown disassembled but in their proper order of assembly.

Referring to the drawings, the thermostatic switch 16 includes a base 11 and a switching mechanism 12. The base 11 is formed from suitable insulating material and carries a nut 13 secured thereto by swaging. A shaft 14 has a theraded portion 15 for engagement with the inner threaded surface of the nut 13. The lower end 16 of the shaft 14 is knurled to hold a knob (not shown) for a manual rotation of the shaft 14 to move the upper rounded end 17 relative to the base 10.

The switching mechanism 12 includes a U-shaped supporting bracket 18 having a lower leg 19 secured to the base 11 by rivets 20. The bracket 18 also has an upper leg 21 which supports a flexible spring element 22, a backing plate 23, a bimetallic member 24, and a clamping plate 25. The spring element 22 and the bimetallic member 24 he generally parallel and have their right ends firmly secured to the upper leg 21 of the supporting bracket 18 by rivets 26.

As shown best in Figure 3, the bimetallic member 24 has two slots 27 extending substantially parallel with the longitudinal edges of the bimetallic member 24 to form a pair of exterior strips 28 and a central strip 29 all integrally joined at each end of, the bimetallic member 24. A hole 30 is provided near the free end of the bimetallic member 24 to receive an electrical contact 31. The bimetallic member 24 as initially formed has a flat shape and in its normally unstressed condition will not function with a snap action.

tes Patent 2 ,835,767 Patented May 20, 1958 The backing plate 23 and the clamping plate 25 each have, respectively, a slot 32 and a slot 33 to provide for free movement of a greater length of the central strip 29 than of the exterior strips 28. The clamping plate 25 has a threaded aperture 34 for receiving a tensioning screw 35 for lateral engagement of its end with the central strip 29 opposite the hole 36 in the backing plate 23. As the end of the tensioning screw 35 is moved toward the backing plate 23, it draws the central strip 29 into the hole 36 and slightly shortens the free or unsupported length of the central strip 29. This places the unsupported end of the central strip 29 in tension and the unsupported ends of the exterior strips 28 in compression. The exterior strips 28 will then be bowed with respect to the central strip 29. By proper adjustment of the tensioning screw 35, the bimetallic member will have a snap action as it flexes from one position to another.

The spring element 22 comprises an elongated piece of relatively thin spring material such as Phosphor bronze. The spring element 22 is formed at 37 such that the supported section 38 normally springs toward the base 11. The free end of the spring element 22 carries on its lower side a contact support 39 of insulating material. Attached to the contact support 39 and positioned in a slot 44) at the free end of the spring element 22 is an electrical contact 41. tached to lead wire 43 is in electrical contact with the contact 41. The free end of the spring member 22 also carries a bracket member 44 attached to the tab portion 45 and having an arm 46 extending over and across the free end of the bimetallic member 24. The bracket member 44 carries a stop screw 47 located in the arm opposite the contact 31 to determine the spacing between contacts 31 and 41 in the open circuit condition.

The lower side of the contact support 39 is held against the rounded end 17 of the shaft 14 at all times by the spring element 22. Rotation of the shaft 14 varies the position of the free end of the spring element 22 in respect to the base 11. Mounted on the backing plate 23 is a calibrating screw 48 which bears against the lower leg 19 of the supporting bracket 18. The calibrating screw 48 determines the spacing between the free ends of the upper and lower legs 19 and 21 of the supporting bracket 18, and accordingly determines the locations of the fixed ends of the spring element 22 and the bimetallic member 23 in respect to the base 11.

For control of an electrical circuit by the thermostatic switch 10, electrical connections may be made to the lead wire 43 and the supporting bracket 18. The circuit through the thermostatic switch 10 may be traced as follows: from the lead wire 43 through terminal 42, contact 41, contact 31, bimetallic member 24, clamping plate 25, and rivets 26 to the supporting bracket 18. The passage of current through the bimetallic member 24 will heat it and hence the thermostatic switch is responsive to both the ambient air temperature and the electric current it controls.

As the temperature of the bimetallic member 24 increases, the exterior strips 28 tend to change their curvature and upon sufiicient increase in temperature change their curvature from convex downwardly to concave upwardly. The change in curvature occurs with a snap action to separate the co-operating contacts 31 and 41. Upon sufficient decrease in temperature of the bimetallic member 24-, the curvature of the exterior strips 28 again reverses to cause the contacts 31 and 41 to engage.

Because the supported end of the bimetallic member 24 is rigidly attached to the supporting bracket 18 and is maintained in a fixed position relative to the base 11, the rounded shaft end 17 hearing against the spring element 22 applies a force on the end of the bimetallic An electrical terminal 42 atmember 24 which affects the curvature of the exterior strips 28. Rotation of the shaft 14 to move its rounded end 17 away from the base 11 decreases the downwardly convex curvature of the exterior strips 2% to decrease the temperature at which the bimetallic member 24 flexes to separate the contacts 31 and 41. Similarly, the contactopening temperature can be increased by rotating the shaft 14 to move its rounded end 17 toward the base 11.

The stop screw 47 carried by the bracket member 44 limits the spacing between the contacts 3?. and 41 in the open circuit position to control the temperature differential between the contact opening and closing temperatures. The stop screw 47 affects the curvature of the exterior strips 28 only while the bimetallic member 24 is in the open-circuit position and has no effect on the contact-opening temperature.

The thermostatic switch 1% is normally operated over a relatively narrow temperature range by limitingthe rotation of the shaft 14 to less than one revolution. The

thermostatic switch 10 may be easily and accurately calibrated by adjustment of the tensioning screw 35 and the calibrating screw 48 to have a predetermined contactopening temperature with the shaft rounded end 17 located at a fixed maximum distance from the base and another predetermined.contact-opening temperature with the shaft rounded end 17 located at a fixed minimum distance from base 11.

The difference in contact-opening temperatures with two given positions of the shaft 14 may be selected by adjustment of the 'tensioning screw 35. Adjustment of the tensioning screw 35 varies the tension stress in the central strip 29 and changes the thermal deflection rate of the bimetallic member 24. By thus adjusting the deflection of the bimetallic member 24 per degree of temperature change, the thermostatic switch It) may be provided with any desired change in contact-opening tem perature for a given change. in position of the shaft 14.

After adjustment of the tensioning screw 35, adjustment of the contact-opening temperature at a specified position ofthe shaft 14 is accomplished by adjustment of the calibrating screw 43. Rotation of the calibrating screw 48 shifts the position of the supported ends of the bimetallic member 24 and the spring element 22 relative to the base 11. Because the free end of the spring element 22 is restained by shaft 1.4 from being shifted a corresponding amount in the opposite direction relative to the base if, rotation of the calibrating .screw 48 adjusts the force applied tothe'free end of the bimetallic member 24 and hence its contact-opening temperature.

While a preferred embodiment of the invention has been illustrated, it should be understood that other modifications and changes may be made without departing from the spirit-and the .scope of the invention as defined in the claims which follow.

What is claimed is:

l. in a thermostatic switch, the combination of a base of insulating material; a substantially U-shaped supporting bracket having first and second legs, said first leg being secured to said base; a flexible spring arm, a backing plate, a bimetallic member, and a clamping plate carried in that order on the secondleg of said supporting bracket; said bimetallic member having two substantially parallel longitudinal slots defining a central strip portion separated from exterior strip portions intermediate the ends of said bimetallic member; a first contact carried by the free end of saidbimetallic member; a second contact carried by the free end of said spring arm for cooperation with said first contact; a stop bracket carried by the free end of said spring arm for limiting movement of the bimetallic member away from the spring arm; said clamping plate carrying a first screw opposite an opening in said backing plate, said first screw bearing at substantially a right angle againstsaid central strip to produce a tension stress in said central strip portion, said tension stress applying a compressive stress in said exterior strip portions to bow said exterior strip portions for producing a snap movement of said bimetallic member; a second screw for moving said second leg relative to said base to adjust the position of said supported ends of said bimetallic member and said spring arm relative to said base; and manually adjustable means carried by said base for adjustably varying the position of the free end of said spring arm relative to said base to adjust the operation of said switch in response to changes in temperature thereof.

2. in a theromstatic switch, the combination of a supporting structure; an elongated bimetallic member having a central and two exterior longitudinally extending strips; clamping means securing one end of said exterior "'us to said supporting structure such that said exterior strips have a shorter effective length than said central strip; and adjusting means carried by said supporting structure and producing a tension stress in said central strip to cause snap movement of said bimetallic member in response to changes in temperature thereof.

3. in a theromstatic switch, the combination of a supporting structure, an elongated bimetallic member having a central and two exterior longitudinally extending strips; fastening means securing one end of said exterior strips to said supporting structure such that said exterior strips have a shorter effective length than said central strip; an adjusting screw laterally bearing against one endof said central strip to produce a tension stress therein; and the ends of said central and exterior strips opposite aforesaid ends being integrally joined for contact controlling snap movement of the bimetallic member in response to changes in temperature thereof.

4. in a thermostatic switch, the combination of a base; a supporting structure carried by said base; a one-piece elongated bimetallic member having a central and two exterior longitudinally extending strips; fastening means securing one end of said strips to said supporting structure such that said exterior strips have a shorter effective length than said central strip the opposite ends of said strips being integrally joined for contact controlling movement; a screw carried by said supporting structure and laterally bearing against said central strip near the end secured to said supporting structure to produce a tension stress in said central strip; said tension stress in said central strip applying a compressive stress in said exterior strips tobow said exterior strips for producing a snap movementof said bimetallic member in response to changes in temperature thereof.

5. In a thermostatic switch, the combination of a base; a supporting structure carried by said base; a one-piece elongated bimetallic member having a central and two exterior longitudinally extending strips; fastening means securing one end of said strips to said supporting structure such that said exterior strips have a shorter effective length than said central strip; the opposite ends of said strips being integrally joined for contact controliing movement, a flexible arm carried at one end thereof by said supporting structure and disposed between said himetallicmember and said base; a stop bracket carried by the free end of said spring arm for limiting movement of the bimetallic member away from the spring arm; a screw carried by said supporting structure hearing at substantially a right angle against said central strip to produce a tension stress in said central strip, said tension stress applying a compressive stress in said exterior strips to bow said exterior strips for producing a snap movement of said bimetallic membenand manually adjustable means carried by said base for moving said spring arnrrelative to said base to adjust the operation of said switch in response to changes in temperature thereof.

6. In a thermostatic switch, the combination of a base; a snapacting bimetallic member supported at one end thereof on said base; a flexible spring arm supported at one end thereof on said base and disposed between said base and said bimetallic member; stop means cooperating with said spring arm and said bimetallic member to maintain the free end of said bimetallic member within a predetermined range of movement; cooperating contact means actuated by said bimetallic member and said spring arm; first adjusting means for adjusting means for adjusting the position of said supported ends of said himetallic member and said spring arm relative to said base; and second adjusting means carried by said base for adjustably varying the position of the free end of said spring arm relative to said base.

7. In a thermostatic switch, the combination of a base; first and second plates mounted upon the base; the first plate carrying a screw disposed opposite an opening in the second plate; a bimetallic member having one end secured between the first and second plates, and having a central and two exterior longitudinally extending strips; the first and second plates each having a slot providing the central strip with a greater effective length than the exterior strips; and said screw hearing at substantially a right angle against the central strip to produce a tension stress therein; said tension stress producing a compressive stress in said exterior strips.

8. ln a thermostatic switch, the combination of a base; a supporting structure carried by the base; a flexible spring arm and a snap-acting bimetallic member each secured at one end to the supporting structure; .stop means cooperating with said spring arm and said bimetallic memher to maintain the free end of said bimetallic member Within a predetermined range of movement; first adjusting means for adjusting the position of the supported ends of the bimetallic member and the spring arm relative to the base; and second adjusting means for adjustably varying the position of the free end of the spring arm relative to the base.

9. In a thermostatic switch, the combination of a base; a substantially U-shaped supporting bracket having first and second legs; said first leg being secured to said base; a flexible spring arm and a snap-acting bimetallic member carried by the second leg of the supporting bracket with said spring arm being disposed between the bimetallic member and the base; a first contact carried by the free end of the bimetallic member; a second contact carried by the free end of the spring arm for cooperative engagement with the first contact; a stop bracket carried by the free end of the spring arm and limiting movement of the bimetallic member away from the spring arm; first adjustable means for moving said second leg relative to the base to adjust the position of the supported ends of the bimetallic member and the spring arm relative to the base; and second adjustable means carried by the base for adjustably varying the position of the free end of the spring arm relative to the base.

0 in a thermostatic switch, the combination of a suplg structure; a bimetallic member having a plulity of strips; clamping plates disposed upon opposite sides of the bimetallic member restraining movement of a portion of one of said strips such that said one strip has a shorter effective length than another of said strips; and means producing a tension stress in said other strip to bow said one strip with respect to said other strip.

ll. The thermostatic switch of claim 10 wherein said means producing a tension stress in said other strip comprise an adjusting screw associated with one of the clamping plates and disposed opposite an opening in the other of said clamping plates; said screw bearing at substantially a right angle against said other strip.

12. The thermostatic switch of claim 10 further characterized by a flexible spring arm attached at one end to said supporting structure and disposed between said supporting structure and said bimetallic member; stop means associated with said spring arm and said bimetallic member limiting movement of the free end of said bimetallic member relative to said spring arm; first adjusting means for adjusting the position of said supported ends of said bimetallic member and said spring arm relative to said supporting structure; and second adjusting means for adjustably varying the position of the free end of said spring arm relative to said supporting structure.

References Cited in the file of this patent UNITED STATES EATENTS 2,289,095 Bletz July 7, 1942 2,320,873 Lee June 1, 1943 2,615,108 Lee Oct. 21, 1952 2,667,565 Wallower Jan. 26, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,835,767 U 1 Robert D. Graf et a1 It is hereby certified that error appears in the -printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 344., for "inevention" read invention line 48,

for "theraded" read threaded colmnn 3, line 45, for "restained" read restrained column 4, lines ll and 21, for "theromstatic"; each occurrence, read thermostatic Signed and sealed this 23rd day of September 1958.

(SEAL) Attest:

KARL H AXLINE ROBERT C. WATSON Attcsting Officer Commissioner of Patents UNITED STATES PATENT oEFIEE CERTIFICATE 9F 'CGRRECTION Patent No. 2 832 767 Robert D Graf et al6 Column 1, line 344., for "inevention" read invention line 48,

for theraded" read m threaded column 3, line 45, for "restained" read restrained --5 column 4, lines 11 and 21, for "theromstatic"; each occurrence, read m thermostatic Signed and sealed this 23rd day of September 1958.

( SEAL Attest:

KARL H AXLINE ROBERT C. WATSON Attesting Ofiicer Commissioner of Patents 

